Optical fiber face-plate assembly for image tubes



, SR BFBBEBGE E. BEHUN April 5, 1966 Filed Feb. 14, 1962 3 19.3 2 9N. 4I. 1.. 2R 30 United States Patent O 3,244,921 OPTICAL FIBER FACE-PLATE ASSEMBLY FOR IMAGE TUBES Eugene Behun, Fort Wayne, Ind., assignor to International Telephone and Telegraph Corporation, Nutley, NJ.,

a corporation of Maryland Filed Feb. 14, 1962, Ser. No. 173,160 11 Claims. (Cl. 313-94) This invention relates generally to vacuum tubes for producing an optical image, such as cathode ray tubes, image intensifier tubes, and image converter tubes, and more particularly to a faceplate assembly of such tubes.

All image ltubes are provided with a viewing screen or output faceplate having a coating of electron-luminescent phosphor on its inner surface, and optical input image tubes additionally have a Window or input faceplate having a photocathode on its inner surface.

There are many instances where it is desired photographically to record the optical image appearing on the output faceplate of an image tube. Where high resolution, maximum light efiiciency, and distortion free transfer of the optical image to film is required, ordinary optical transfer of the image is not suitable since high speed lenses invariably suffer from loss of resolution and image distortion, and additionally can only intercept a small portion of the total radiation emitted by the phosphor on the interior surface of the faceplate. In order to maximize the efficiency of image transfer, image tubes have been provided with an extremely thin mica sheet for the output faceplate of a tube with the recording film then being pressed into intimate contact with the outside surface of the mica sheet or window. In this manner, substantially all the light generated in the phosphor on the inner surface of the mica sheet is captured on the film; high resolution is maintained since the film is separated from lthe phosphor only by the thickness of the thin mica sheet. In prior image tubes of this type known to the present applicant, however, the diameter of the mica faceplate has been restricted since the tube is evacuated and thus the thin mica faceplate must sustain a relatively high pressure differential. Thus, in such prior image tubes employing mica output faceplates having a thickness on the order of 9A@ mil, the diameter has been restricted to on the order of 1/2 inch; even at this diameter, curvature of the faceplate due to the vacuum loading causes some difficulty in recording because the photographic film must be curved to conform with the faceplate in order to maintain good resolution in the recording.

It is desirable to provide an image tube having a mica output faceplate of greater diameter and to this end, efforts have been made to provide a grid support structure for the thin mica faceplate. However, even in instances Where such a grid support structure is tolerable from the standpoint of image obstruction, the pressure loading across each segmental area of mica sheet defined by the grid support structure causes a compound curvature of the mica sheet, and since the film cannot conform to these deflections, the resolution of the image recorded thereon suffers.

In the case of optical input image tubes, it is almost mandatory that the photocathode surface be convex and the entire input faceplate therefore generally has been curved. In such constructions, the optical image is placed on the curved input faceplate by providing an external field curving lens which however limits the effective speed of the input optics. It is therefore further desirable to provide an optical input image tube having an input faceplate with a at external surface and a convex inner surface so that the input optics may place a flat image on the external surface.

The use of fiber optics faceplates suggests itself as a solution to the problem. Optical fibers are essentially small diameter rods of transparent dielectrical material. Light conduction along transparent rods is well-known and when a large number of such rods are sealed together in the form of a sheet having one or both opposite sides flat and with the fibers extending transversely between the sides, an optical image is conveyed from one side to the other with high light eiciency. It has been proposed to employ such a liber optic sheet for the faceplate of an image tube with the phosphor being applied directly to one side -thereof which would in turn permit application of the recording film directly to the other side. Such fiber optic sheets can be made relatively thick compared with prior mica faceplates, are self-supporting, and this would appear to eliminate the pressure differential problem which has restricted the diameter of the faceplates of image tubes employing mica as the faceplate material. However, difficulty has been encountered in securing a vacuum-tight seal between such a fiber-optic faceplate and the tube blank.

It is accordingly an object of my invention to provide a mica faceplate construction for an image tube wherein the diameter of Ithe faceplate may be substantially greater than heretofore provided in prior image tubes having mica faceplates.

Another object of my invention is to provide a faceplate construction for an image tube having a flat external surface and a convex inner surface.

A further object of my invention is to provide an improved image tube construction incorporating a fiber optics faceplate.

Yet another object of my invention is to provide an improved vacuum-tight seal for an image tube incorporating a fiber optics faceplate.

In accordance with the broader aspects of my invention, therefore, there is provided a tube blank having an open end with a fiber-optic sheet supported within the blank and mechanically closing the open end, the fiberoptic sheet having a fiat outer side. A sheet of relatively thin, optically transparent, impervious material, such as mica, is provided overlaying the -at outer side of the fiber-optic sheet and sealed to the blank in vacuumtight relationship. With this construction, the fiber-optic sheet need not have a vacuum-tight seal with the tube blank, but on the contrary is merely mechanically supported in the proper location. The vacuum seal is pro vided by the mica window which is supported over substantially its entire area by the underlying fiber-optic sheet or faceplace. A at external surface is, therefore, presented which in the case of the output faceplate permits direct application of the recording film for simple contact exposure and in the case of the input faceplate permits application of a flat optical image, the size of the resulting faceplate assembly being limited only by the availability of large-area sheets of mica of the requisite -thinness.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and 4the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawing wherein the single figure of the drawing is a cross-sectional view of an image tube employing the invention.

Referring now to the drawing, there is shown an image tube, generally indicated at 1, of the type employed for converting a radiation image from one spectrum to another, i.e., for example from infra red to visible light. |Ihe tube 1 comprises a blank or body portion 2, shown as being formed of glass in accordance with conventional practice, the body 2 being closed at one end by an input window or faceplate assembly 3 to be hereinafter more fully described, with a conventional photocathode 4 formed on its inner surface; photocathode 4 emits electrons in response to impingement of a radiation image thereon.

The other end 5 of blank 2 is closed by an output faceplate assembly, generally indicated at 6, to complete the evacuated enclosure. Output faceplate assembly 6 comprises a first metallic supporting ring 7 having one end 8 sealed in the end 5 of the 4blank 2 in accordance with conventional practice. Ring 7 extends axially from end 5 of the blank 2 and has a radially inwardly extending annular flange 9 formed on its other end. A second support ring 10 is provided having a radially inwardly extending annular flange 1'1 formed at one end, the flanges 9 and 11 being arranged in abutting relationship, as shown, and being sealed together in vacuum-tight relationship, as by a seam weld 12.

Mechanically supported within the support ring 10, but not fused or otherwise sealed thereto, is a fiber-optic sheet or plate 13 having flat opposite sides 14 and 15 and with the fibers extending generally transversely lbetween the sides. A conventional phosphor layer 16 is coated or deposited on the inner side 14 of the fiber-optic sheet 13 and produces a visible image when electrons emitted from photocathode 4 impinge thereon. It will be readily understood that suitable potentials will be applied to the photocathode 4 and phosphor layer 16 and that suitable accelerating electrodes may be provided within the envelope 2, as is well known to those skilled in -t-he art.

Abutting the outer side 15 of the fiber-optic sheet 13 and supported thereby is a relatively thin sheet 17 of suitable impervious transparent material, such as mica. Support ring 10 has a radially outwardly extending flange 18 spaced axially from ange 11. Abutting flange 18 and secured thereto in vacuum-tight relationship by a seam weld 19 is a radially inwardly extending support ring 20; ring 20 is seated in an annulargroove 21 formed in the fiber-optic sheet 13 so that the outer surface of ring 20 is flush with the outer side 15 of sheet 13. Sheet 17 in turn extends onto the outer surface of ring 20 and is sealed thereto in vacuum-tight relationship, or at 22. It will be seen that photographic film in roll form can be transported past the sheet 17 in abutting relationship therewith for successive recordings.

It will nolw be seen that with the output faceplate c0n`- struction of the invention, the fiber-optic faceplate 13 is not required to be fused or sealed within the support ring 10, but is merely mechanically supported therein, and it will further be seen that the mica sheet 17, Which can be con veniently sealed to the flange 20 of support ring 1S by techniques well known to those skilled in the art, completes the vacuum-tight seal for the tube. With suc-h a construction, output faceplate diameters as great as three or four inches may be provided with the ber-optic sheet 13 having a thickness from 1/10 to l; inch and with a mica sheet 17 having a thickness on the order of 3/10 mil.

The input faceplate assembly 3 comprises a metallic supporting ring 23 having one end sealed in end 24 of blank 2 and having a radially inwardly extending annular ange 25. Another support ring 26 is provided having a radially inwardly extending annular ange 27, anges and 27 being sealed together by a seam weld 28. Another fiber-optic sheet or plate 29 is mechanically supported within support ring 26, but again is not fused or sealed thereto. Fiber optic sheet 29 has a fiat external surface 30 and a concave internal surface 31 on which photocathode 4 is deposited.

Another support ring 32 is provided telescoped within support ring 26 and sealed thereto in vacuum-tight relationship by a seam weld 33. Support ring 32 has a radially inwardly extending annular flange 34 thereon adjacent the outer surface 30 of the beroptic sheet 29. A relatively thin sheet 35 of suitable impervious material, such as mica, abuts the outer surface 30 of sheet 29 and is supported thereby. Sheet 35 has its perimeter sealed to ange 34 of ring 32 in vacuum-tight relationship. It will be seen that the input faceplate construction of this invention provides a at external surface and the requisite intemal-ly convex surface, it being far easier and less costly to form the convex surface 31 in fiber-optic sheet 29 than to grind such a convex surface in a glass sheet.

While mica is eminently suited for use as the sealing sheets 17 and 35, any 4other optically transparent impervious material `which can be provided in a sheet of the requisite thinness and which will withstand the high ternperatures required during bake-out of the tube, such as glass, may be employed.

While the input faceplate assembly 3 has been shown in connection with an optical-output image tube, it will be readily apparent that it may be employed in electrical output tubes such as an image dissecter tube. Likewise, while the output faceplate asesmbly has Ibeen shown in connection with an optical-input tube, it may be employed equally advantageously with an electrical input tube, such as a cathode ray tube.

It will be understood that the fiber-optic material from which the sheet 13 is formed is not my invention, such fiber-optic materials being described in numero-us technical articles including an article entitled, Fiber Optics," by Narinder S. Kapany, appearing in Scientific American of November 1960.

While an image converter tube has been shown and described, it will be readily yapparent that the invention is equally applicable to other types of image tubes including cathode ray tubes, and image intensifier tubes.

It w1 t e seen that the invention permits the direct application of recording film to the faceplate 'of an image tube, thus eliminating further `optics and the resulting loss of efficiency and resol-ution and permitting much higher speed than conventional optics in a tube having a faceplate diameter substantial-ly greater than has heretofore been possible employing mica alone as the faceplate material.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention.

What is claimed is:

1. In an image tube comprising a tube blank having an open end and a face plate assembly closing said end, said assembly including a fiber-optic end plate having inner and outer sides, means sealed to said open end in a vacuum-tight relationship, said means supporting said plate across said open end in an abutting relationship, and a sheet of relatively thin impervious transparent material overlaying the outer side of said liber-optic end plate and supported thereby in an abutting relationship, the perimeter of said sheet being sealed to said supporting means in vacuum-tight relationship.

2. In an image tube: an evacuated envelope having a body portion with an open end and a faceplate assembly closing the same, said assembly comprising an extended area self-supporting fiber-optic sheet having inner and outer sides with the fibers thereof extending generally transversely between said sides, an image producing layer on said inner side thereof, at least the outer side of said sheet being flat, a supporting member sealed to and extending from said open end of said body portion in vacuum-tight relationship, said member mechanically supporting said fiber-optic sheet within said member across said open end in an abutting relationship, and a sheet of relatively thin impervious optically transparent material abutting said outer side of said fiber-optic sheet and supported thereby, said transparent sheet having its perimeter sealed to said supporting member in vacuum-tight relationship.

3. In an image tube: an evacuated envelope having a body portion with an open end and a faceplate assembly closing the same, said assembly comprising an extended area self-supporting ber-optic sheet having inner and outer sides with the fibers thereof extending generally transversely between said side, an image producing layer on said inner side thereof, at least the outer side of said sheet being flat, a metallic supporting ring sealed to said open end of said body portion in vacuum-tight relationship and extending axially therefrom, said fiber-optic sheet being mechanically supported by without being sealed thereto, and a sheet of optically transparent material abutting a substantial portion of the surface area of the outer side of said sheet and ybeing supported thereby, said transparent sheet having its perimeter sealed to said supporting member in vacuum-tight relationship.

4. The combination of claim 3 wherein said transparent sheet is formed of mica.

5. In an image tube: an evacuated envelope having a glass body portion with an open end and a faceplate assembly closing the same, said assembly comprising an extended area self-supporting fiber-optic sheet having inner a-nd outer sides with the bers thereof extending generally transversely between said sides, an image producing layer on said inner side thereof, at least the outer side of said sheet being flat, a rst metal support ring having one end sealed to said open end of said body portion in vacuum-tight relationship and extending axially therefrom, said 4El'lrst ring having -a radially inwardly extending annular flange portion formed at its other end, a second metal support ring having a radially inwardly extending annulary flange portion formed at one end, said flange portions being abutting and sealed together in Vacuum-tight relation, said fiber-optic sheet being mechanically supported within said second support ring adjacent the flange thereof without being sealed thereto, a third metal support ring adjacent the outer side of said liber-optic sheet, said second and third rings being sealed together in vacuum-tight relationship, and a sheet of relatively thin mica abutting a substantial portion of the surface area of said other side of said ber-optic sheet and supported thereby, said mica sheet having its perimeter sealed to said flange of said third ring in vacuum-tight relationship.

6. The combination of claim 3 wherein both sides of said fiber-optic sheet are at and respectively parallel.

7. The combination of claim 3 wherein both sides of said ber-optic sheet are flat and respectively parallel, and wherein said image producing layer comprises a relatively thin phosphor coating.

8. The combination of claim 3 wherein said inner side of said fiber-optic sheet is concave.

9. The combination of claim 8 wherein said image produci-ng layer comprises a photocathode.

10. In an image tube: an evacuated envelope having a glass body portion with an open end and a faceplate assembly closing the same, said assembly comprising an extended area self-supporting fiber-optic sheet having inner and outer sides with the fibers thereof extending generally transversely between said sides, an image producing layer on said inner side thereof, at least the outer side of said sheet being flat, a rst metal support ring having one end sealed to said open end of said body portion in vacuum-tight relationship and extending axially therefrom, said first ring having a radially inwardly extending 'annular flange portion formed at its other end, a second metal support ring having a radially inwardly extending annular flange portion yformed at one end, said llange portions being abutting and sealed together in vacuumtight relation, said fiber-optic sheet being mechanically supported within said second support ring adjacent the tlange thereof without being sealed thereto, a third metal support ring abutting said second ring and sealed thereto in Vacuum-tight relationship, said third ring extending radially inward and having an outer side flush with said outer side of said fiber-optic sheet, a-nd a sheet of relatively thin mica abutting said outer side of said fiberoptic sheet and supported thereby, said mica sheet having its perimeter sealed to said third support ring in vacuumtight relationship.

11. The combination of claim 3 wherein -a pair of fiber optic sheets and transparent sheets enclose both ends of said envelope, one end including a concave inner side having a photocathode layer and the other end including a ilat inner side having a phosphor layer.

References Cited by the Examiner UNITED STATES PATENTS 2,979,632 4/ 1961 MacNeille 313-89 3,033,07-1 5/ 1962 Hicks 88-57 3,058,021 10/ 19612 Dunn 88-1 OTHER REFERENCES Article by Morton and Ruedy, Image Intensier; RCA TN No. 268, June 29, 1959.

GEORGE N. WESTBY, Primary Examiner.

ARTHUR GAUSS, Examiner.

C. O. GARDNER, R. SEGAL, Assistant Examiners. 

1. IN AN IMAGE TUBE COMPRISING A TUBE BLANK HAVING AN OPEN END AND A FACE PLATE ASSEMBLY CLOSING SAID END, SAID ASSEMBLY INCLUDING A FIBER-OPTIC END PLATE HAVING INNER AND OUTER SIDES, MEANS SEALED TO SAID OPEN END IN A VACUUM-TIGHT RELATIONSHIP, SAID MEANS SUPPORTING SAID PLATE ACROSS SAID OPEN END IN AN ABUTTING RELATIONSHIP, AND A SHEET OF RELATIVELY THIN IMPERVIOUS TRANSPARENT MATERIAL OVERLAYING THE OUTER SIDE OF SAID FIBER-OPTIC END PLATE AND SUPPORTED THEREBY IN AN ABUTTING RELATIONSHIP, THE PERMITER OF SAID SHEET BEING SEALED TO SAID SUPPORTING MEANS IN VACUUM-TIGHT RELATIONSHIP. 